Usually, an internal combustion engine, particularly if it is employed in a motor vehicle, comprises a piston engine, which comprises at least one combustion chamber and a fresh air system for feeding fresh air to the at least one combustion chamber. This fresh air system comprises at least one fresh air line in which a fresh air flow is conducted in the direction to the respective combustion chamber.
In the case of charged internal combustion engines, wherein in the fresh air system a charging device is arranged, a pre-ignition can occur at low rotational speeds and high loads, which constitutes a damaging hazard for the piston engine. Such a pre-ignition can, in particular, occur with petrol engines with direct injection. In the case of such a pre-ignition, the fuel-air mixture self-ignites during the compression, that is before the regular combustion can be initiated by means of an ignition spark. In this, the pre-ignition differs from the so-called knocking, with which a self-ignition of the as yet uncombusted mixture takes place only after the regular ignition. Possible courses for the pre-ignition are among other things so-called hot spots, i.e. localised regions in the respective combustion chamber which because of an inhomogeneous temperature distribution have a higher temperature relative to their surroundings, which can trigger the ignition.
Furthermore, for reducing pollutant emissions, it is generally known to recirculate exhaust gas from an exhaust system of the internal combustion engine into the fresh air system. Important in this context is an intensive mixing-through between fresh air and recirculated exhaust gas before the fresh air-exhaust gas mixture enters the respective combustion chamber.